The present invention relates to a semiconductor device, and more particularly, to a fuse which is included in a highly integrated semiconductor device.
Generally, a fuse is defined as a type of an automatic circuit breaker which is used to prevent over-current from continuously flowing through an electric line. That is, a fuse melts itself with heat generated by the over-current to cut off the electric line, which can be easily found in common electrical appliances.
A fuse allows current to keep flowing during normal operation. However, once a fuse is cut off, it permanently interrupts the flow of electric current until it is replaced with a brand new one. This differentiates the fuse from a switch which is capable of controlling whether to let current flow or not.
A semiconductor device is manufactured by injecting dopants into a certain region in a silicon wafer or by depositing a new material on it in order to operate by its intended purpose.
A typical example includes a semiconductor memory device. Also, a semiconductor device can include a transistor, capacitor, resistor, and many other components as well as a fuse to perform its intended functions.
A fuse is used in various parts of a semiconductor memory device, for example, a redundancy circuit, a power supply circuit and the like. Fuses used in such circuits are made normal (i.e., unblown) during a manufacturing process, but after that, they can be selectively blown (i.e., cut) during a testing process.
For example, to illustrate more precisely a redundancy circuit, it is subjected to a recovery step to replace some defective unit cells in the semiconductor memory device with redundant cells.
If an address to access a defective unit cell is inputted from outside, the recovery step allows a redundant cell to be accessed instead of the defective unit cell, and stores an address of the defective unit cell to prevent access to the defective unit cell.
The most commonly used component in this recovery step is a fuse. A fuse is cut off permanently by irradiating a laser on the corresponding fuse in a semiconductor device and blowing it. This process is so called “fuse-blowing.”
A semiconductor memory device includes a plurality of unit cells, and it is impossible to identify which unit cell might be defective before a manufacturing process. Thus, a fuse box having a plurality of fuses is included in a semiconductor memory device to replace any defective unit cell within a semiconductor memory device with a redundant cell.
Data storage capacity of a semiconductor memory device is increased more and more. Consequently, the number of unit cells included in the semiconductor memory device is increased, so that the number of fuses is also increased.
On the other hand, a higher degree of integration is required as the entire area of a semiconductor device is reduced. As described above, some of fuses are physically “blown” by selectively irradiating a laser thereon. Therefore, fuses must be separated from each other with a given space to protect neighboring fuses from being unintentionally blown by a laser. However, this may cause the degree of integration in a semiconductor memory device to be lowered.
FIGS. 1 and 2 are views illustrating a fuse in a conventional semiconductor device.
DRAM uses a redundancy cell for replacing defects of a main cell by blowing fuses. Fuses for use in the prior art are formed in a row inside a rectangular fuse box 1 as shown in FIGS. 1 and 2. In addition, the fuses 2 are cut by irradiating a laser on the corresponding fuses 2.
At this time, in the prior art, laser energy is used for cutting a fuse. However, in this process, diffused reflected laser or explosion of the target fuse can cause damage to adjacent fuses, which may lead to defects of these fuses.
Also, after chips are mounted on a substrate and electrically connected to the substrate, a semiconductor package is sealed by epoxy molding compound (EMC) to protect the chips and the substrate.
However, there is a problem that fuses may collapse or crack due to the stress from applying EMC or other package coating material in a subsequent packaging process.